The invention relates to processes for etching a silicon film on a workpiece. More specifically, the invention relates to processes for selectively etching silicon without etching silicon oxide or silicon nitride.
Electronic devices containing silicon-based semiconductors, such as integrated circuits and flat panel displays, generally are fabricated by depositing many successive layers of silicon, metal and dielectric and patterning the layers to form various electronic circuitry components such as transistors, resistors, capacitor, and interconnect conductors.
The most commonly used dielectric materials are silicon oxide and silicon nitride. Silicon layers can function as semiconductors or conductors depending on their level of impurity doping.
To form the desired electronic component structures, it is necessary to etch a pattern in one layer of material without etching adjacent layers. However, most etch processes intended to selectively etch one specific material, such as silicon, unavoidably etch to some extent layers of other materials, such as silicon oxide or silicon nitride, that are adjacent to or underlying the layer that is intended to be etched.
Selective etch processes can be characterized by a selectivity ratio, which is the ratio between the amount of desired material removed to the amount of undesired material removed by the etch process per unit time. An etch process generally will have different selectivity ratios relative to different undesired materials. High selectivity is very difficult to achieve.
Therefore, a need exists for a process for selectively etching silicon without etching silicon oxide or silicon nitride.
The invention is a process for selectively etching silicon without etching silicon oxide or silicon nitride. The principal etchant gas is molecular fluorine gas (F2) that is not excited to a plasma state.
I discovered that, when not decomposed in a plasma, molecular fluorine gas effectively etches silicon without etching silicon oxide or silicon nitride to any measurable extent. Therefore, a silicon etch process using molecular fluorine can achieve essentially infinite etch selectivity relative to silicon oxide and silicon nitride.